Telephone system



Oct. 24, 1939. F. KESSLER 2,177,069

TELEPHONE SYSQPEM r1104 P. s, 1938 10 Sheets-Sheet 1 FIG. 1 1

WAY

FTUTOMATIC EXCHANGE l I FINDER swncnswncH I FINDER ECT I SWITCH SWITCH182 as I AUTOWtTCI-W'? OMATIC SWITCHING EQUIPM INVENTOR. FRANK KESSLERATTORNEY.

Och 24, 1939. F, ss 2,177,069

TELEPHONE SYSTEM Filld F010. 3, 1938 lo Sheets-Sheet 2 Have W C1236 RA43 c1237 RA244 C1238 RA 45 INVENTOK FRANK KESSLER ATTORNEY.

0d. 24, 1939. F ss 2,177,069

TELEPHONE SYSTEM Filod Feb. 3, 1958 10 Sheets-Sheet 4 FRANK KESSL ERATTORNEY.

0d.- 24, 1939. KESSLER 2,177,069

TELEPHONE SYSTEM 7 I Filld FQb. 3, 1938 10 Sheets-Sheet 5 7 HI TIT III:1: u C 2. m

(z o ru m INVENTOR. FRANK KESSLER A TTORNEY;

Oct. 24, 1939. KESSLER I 2,177,069

TELEPHONE SYSTEM Filed Feb. 3, 1958 10 Sheets-Sheet 7 [N6 RELAY m I g; af I\ 2 as j - h INVENTOR.

d FRANK KESSLER BY E v ziag,

ATTORNEY.

Oct F. KESSLER I 2917479069 TELEPHONE SYSTEM F1104 Feb. 3, 1958 10Sheets-Sheet 8 ALARM APPARATUS FIG. 8

BUSY 13 DIAL TONE APPARATUS meme APPARATUS FRANK KESSLER ATTORNEY;

BY r

Patented-Oct. 24, 1939 2, 77,0 9

UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Frank Kessler, Villa Park,111., assignor to Associated Electric Laboratories, Inc., Chicago, 111.,a corporation of Delaware Application February 3, 1938, Serial No.188,443 38 Claims. 179-18) The present invention relates to telephonerelay type which is fully directive in character.

systems, and more particularly to small auto- Another object of theinvention is to provide matic telephone systems of the type adapted forin a telephone system including a plurality of installation in smalltowns or villages. finder switches, improved allotter or distributor Anautomatic telephone system of the charequipment associated with thefinder switches for acter noted is generally known as a communityassigning in a predetermined order idle ones of automatic exchange or C.A. X and usually has the finder switches to the use of calling lines.

a line capacity of one hundred lines or less. For A further object ofthe invention is to provide reasons of economy, the lines are usually ofthe allotter or distributor equipment associated with 10 multi-partytype and code ringing is utilized for the finder switches of a telephonesystem which 10 selectively signaling the telephone stations on s Ope be t ass an idle One Of t e finde the various subscriber lines. In orderto proswitches to the use of the next calling line immevide toll serviceto the subscribers, provisions are diately after a previously assignedone of the also made for trunking calls to and from one or finderswitches selects a calling line and to pre- 5 more distant exchanges.One improved all-relay vent the assignment of the previously assignedtelephone exchange of t type is disclosed and finder switch as long asthe selected calling line claimed in the copending application SerialNo. is busy, and an improved arrangement respon- '86,046, (Norman H.Saunders), filed June 19, sive to a fault in one of the finder switchesfor 1936. causing operation of the allotter or distributor 'In brief, inthe system as disclosed in the equipment to prevent the assignment oftheme 30 above-mentioned Saunders application, the subfinder switch.scriber and trunk lines extend to the finder and Another object oftheinvention is to provide connector switches of each of a, plurality ofallin a telephone system, a numerical switch havrelay finder-connectorlinks,vcommon equipment 118 access to a plurality of trunk nd s c ibeincluding a relay type-link distributor or allotter lines, and includingimproved PD 'QWS 0- 25 being provided for assigning idle ones 01' thlinks tively controlled in accordance with diilerent to successivecalling lines in a predetermined relations between the line selectingdigits for order. The finder switches of the various links causing theoperation of the numerical switch are semi-directive in character; thatis, it is to provi e trunk and u s r line c O necessary to hunt for thecalling line in a pre- A further object of the invention is to providean viously marked group of lines during the operain a numerical switchhaving access to a group tion of a link to seize the calling line.Although of lines including subscriber and trunk lines an thisarrangement is entirely satisfactory from improved arrangement forcausing operation 01 an operating standpoint, a substantial interval theswitch to select a particular one of the of' time is consumed by thefinder switch in subscriber lines or for causing operation of the 35hunting the calling line in the previously marked switch to select apreviously selected idle one of group of lines. Provisions are also madein the the trunk lines, and improved apparatus resystem of the Saundersapplication for testing a sponsive to the selection of the one trunkline selected line to determine the idle. or busyconfor immediatelyselecting anothenidle one of the 40 dition thereof, for applying busytone current trunk lines for use. n to a calling line in the event theselected called The fea ur s of h Present nti n are line is bus and forapplying coded ringing illustrated as being incorporated in a telephonecurrent to a called multi-party subscriber line exchange having anultimate capacity of one in the event the selected called lineis idle inhundred lines. The lines are arranged ina order to signal a particulartelephone station plurality of groups of ten lines each of which 45connected thereto. is individually divided into'two subgroups of It isan object of the present invention to profive lines each, certain of thelines being twovide, in a telephone system of the character wayinter-ofllce trunk lines, others of the lines noted, an improved linefinder switch of the being private exchange or P. B. X trunk lines,

all-relay type which requires a minimum numand the remainder of thelines being subscriber 50 her or relays both in the switch itself and inlines. The various lines individually terminate .the associated commonequipment. in line circuits which are connected in the same It isanother object of the invention to promanner regardless of whether aline is a trunk vide, in a telephone system of the character or asubscriber line. The telephone exchange 5 noted. an improved line finderswitch of the allalso includesv a plurality of finder-connector andresults in a considerable reduction in invention, the

links which individually have access to the lines, and allotter ordistributor apparatus for assigning, in a predetermined order, idle onesof the links to the use of the calling lines.

In accordance with one feature of the invention, each of the finderswitches includes a plurality of group relays, a group of unit relays,and a subgroup relay, eachof the group relays being operative to selecta corresponding group of lines, and each of the unit relays beingoperative to select-a corresponding line from each of the subgroups,depending upon the operated or non-operated condition of the subgrouprelay. More specifically, each group of lines is divided into twosubgroups respectively comprising odd and even numbered lines and thearrangement is that, when a call is initiated on an odd line, thecorresponding group and unit relays operate, without operating thesubgroup relay, in the finder switch of the assigned link to select the-On the other hand, when a call odd calling line. is initiated on an evenline, the corresponding group and unit relays and the subgroup relayoperate in the finder switch of the assigned link to select the evencalling line. This arrangement reduces the number of unit relaysrequired in each finder switch by approximately one-half themanufacturing cost of the finder switches.

In accordance with a further feature of the group relay and the unitrelay in a finder switch of an assigned link are arranged to operatesubstantially simultaneously to select a line in one of the subgroups;and the group relay, the unit relay and thesubgroup relay in the finderswitch of an assigned link are arranged to operate substantiallysimultaneously to select a line in the other of the subgroups. This isaccomplished by providing common equipment for controlling the operationof a control relay provided in each of the finder switches. Moreparticularly, the common equipment comprises a group of first auxiliaryrelays individually corresponding to a particular group of lines and toa particular group relay in each finder switch, a group of secondauxiliary relays individually corresponding to a particular line in eachsubgroup of lines and to a particular unit relay in. each finder switch,and a third auxiliary relay corresponding to one of the subgroups ineach group of lines and to the subgroup relay in each finder switch.With this arrangement and when a call is initiated on a particular linein one of the subgroups, the corresponding first and second auxiliaryrelays in the common equipment are operated and cause the correspondinggroup and unit relays in the finder switch of the assigned link to beconditioned to, be operated. Also, the second auxiliary relay in thecommon equipment causes theoperation of the control relay provided inthe finder switch of the assigned link, which latter relay causesthepreviousiy conditioned group and unit relays in .the finder switch ofthe assigned link to operate substantially simultaneously, thereby toselect the calling line. When a call is initiated on a line in the otherof the subgroups, the corresponding first and second auxiliary relaysand the third auxiliary relay in the common equipment are operated. Thefirst and second auxiliary relays in the common equipment condition thecorresponding group and unit relays in the finder switch of the msignedlink to be operated, and

' the third auxiliary relay in the common equipment conditions thesubgroup relay in the finder ment renders the finder switch fullydirective and reduces the time required in extending a connection from acalling line to an idle link.

For the purpose of assigning, in a predetermined order, idleones of thefinder switches to the use of calling lines, there is provided, inassociation with the severallinks, allotter or distributor equipmentincluding a group of allotter relays individually corresponding to thelinks.

In accordance with a further feature of the invention, each of theallotter relaysis provided with operating and holding circuits forenergizing the same, and circuits controlled by the operation of theallotter relay also being provided for assigning idle ones of the finderswitches to the use of the lines having a calling condition thereon, andfor preventing the assignment of the corresponding finder switch to theuse of the lines having a calling condition thereon. More particularly,the arrangement is suchthat when one of the finder switches operates toselect aline having a calling condition thereon, the operating circuitof the corresponding allotter relay is completed. Upon operating, theallotter relay completes its holding circuit, assigns an idle one of thefinder switches to the use of the next line having a calling conditionthereon, and prevents the assignment of the corresponding finder switchto the use of lines having a calling condition thereon. Idle ones of thefinder switches are operated successively until the last finder switchin the group is taken for use by a calling line. At this time theholding circuits of all of the allotter relays are interrupted and thoseallotter relays corresponding to idle finder switches restore to recyclethe idle finder switches for use by the lines'having a calling conditionthereon.

In accordance with a still further feature of the invention, anarrangement is provided in association with each of the allotter relaysfor operating the same in response to the presence of a fault in thecorresponding finder switch, in

pears in one of the finder switches, the fuse linkindividual thereto isoperated or blown, causingv the. additional operating circuit of thecorresponding allotter relay to be completed. Upon operating, thecorresponding-allotter relay prevents the assignment of the finderswitch having a fault therein to the use of one of the lines having acalling condition thereon.

In accordance with another feature of the invention, each numerical orconnector switch of each link is provided with apparatus, including agroup of impulse counting relays for causing operation of the numericalswitch to provide trunk and subscriber line selection in an improvedmanner.- More particularly, the apparatus is responsive to apredetermined digit and a predetermined digit following thefirst-mentioned digit for causing the operation of the the linksincluded in the switch to select a particular subscriber line, and isresponsive to the first-mentioned digit and a different predetermineddigit following the firstmentioned digit for causing the operation ofthe switch to select an idle one of a certain group of trunk lines. y

In accordance with a still further object of the invention, an improvedarrangement is provided in conjunction with the last-mentioned group oftrunk lines for assigning idle ones of the trunk lines to be selected bythe numerical switches in a predetermined order. This arrangement issuch that an idle one of the trunk lines is assigned for the use of thenumerical switches immediately following the seizure of a previouslyselected one of the trunk lines by one of the numerical switches.

Further features of the invention pertain to a particular arrangement ofthe circuit elements whereby the above-outlined and additional op--erating features are attained.

The novel features believed to be characteristic of the invention areset forth in the appended claims. The invention, both as to itsorganization and method of operation, together with further objects andadvantages thereof, will best be understood by reference to thespecification, taken in connection with the accompanying drawings, inwhich Figure 12 illustrates the general arrangement of a systemembodying one form of the present invention; Fig. 9 fllustrates the modeof combining the remaining figures of the drawlugs to form a unifiedsystem; and Figs. 1 to 8, inclusive, 10 and 11, illustrate the detailsof a system having incorporated therein the features of the invention asbriefly outlined above.

Referring now more particularly to Fig. 12 of the drawings the telephonesystem there illustrated comprises a small community automatic exchangeI8, a second automatic exchange I85, and a third automatic exchange I88.The exchanges I85 and I86, respectively, are connected to the exchangeI8 by first and second groups, respectively, of two-way-inter-ofllcetrunk lines. One of the first group of inter-oflice trunk lines isindicated at 2i as terminating at a repeater I81; and one of the secondgroup of inter-orifice trunk lines is indicated at 3| as terminating ata repeater I88, the repeaters I81 and I88 forming parts of the apparatuslocated at the exchange I8. Also extending to the exchange I8 are twogroups of private branch exchange or P. B. X trunk lines, not shown,which are accessible to the finder and connector switches of the linksincluded in the exchange I8. Also extending to the exchange I8 are aplurality of subscriber lines, two of which are indicated at 28 and 38.Each of the enumerated subscriber lines .is illustrated as being of themulti-party type having two or more telephone stations associatedtherewith. Thus, two telephone stations, IB and 2B are diagrammaticallyshown as being connected to the line 28, and two additional stations, IDand 21),

are diagrammatically shown as being connectedto the line 38. Each of thesubstations connected to the'various subscriber lines may comprise theusual hand set having embodied therein a conventional dial-controlledimpulsing device. Each of the lines extending to the'Lchange I8 terminates in a line circuit through which it is rendered accessible to thefinder and connector switches of line 28 terminates at a line circuit28', through which it is connected to the contact springs of a finderswitch 288 and to the contact springs of the exchange. Thus, the Iconnector switch 588 which two switches are connected together by linklines to form a finderconnector link. Similarly, the line 38 terminatesat a line circuit 38'; and the illustrated two-way trunk lines 2| and 3|interconnecting the exchange I8 and the exchanges I85 and I86,respectively, terminate at line circuits 2| and 3i, respectively.

As many as ten telephone stations may be connected to each multi-partysubscriber line, these telephone stations being arranged in two groupscomprising five telephone stations each. The signals or ringers of oneof the groups of telephone stations are connected between one side ofthe subscriber line and ground, while the ringers of the other group oftelephone stations are connected between the other side of thesubscriber line and ground, thereby providing an arrangement utilizingdivided ringing.

As indicated above, the exchange I8 is designed to serve a relativelysmall number of lines comprising two groups of inter-ofiice trunk lines,two

. groups of P. B. X trunk lines, and a plurality of subscriber lines,these lines being arranged in ten groups of ten lines each. Accordingly,all of the trunk and subscriber lines are arranged to be served by anyone of a plurality of finder-connector links included in the exchangeI8. Obviously, the number of links required for satisfactory servicewill depend upon the volume of telephone traflic, but, taking intoaccount the character of the exchange, ten links are considered adequatefor reasonably good service. In order to assign the links to successivecalling lines in a predetermined order, so that a link is alwaysavailable for the use of a calling line, excepting, of course, thoseinstances when all of the links are simultaneously busy, there isprovided in association therewith common equipment indicated at I whichincludes a link distributor or allotter. The several links also haveassociated therewith common, ringing tone and timing apparatus which isdiagrammatically shown at 888.

The operation of the system to extend a call initiated at any one of thetelephone stations to another of the telephone stations is describedbriefly below, neglecting the details of the circuit arrangement. Inextending a.- call initiated at one of the telephone stations to one ofthe telephone stations connectedto a subscriber line included in thesecond, third, fourth, fifth, sixth or seventh group of ten lines, acorresponding tens digit, a corresponding units digit and acorresponding code ringing digit are dialed, in the order named, at thetelephone station when the call is initiated. For'example, when asubscriber at the telephone station IB connected to the line 28initiates a call, by lifting his receiver from its switch hook, which isto be extended to the telephone station ID connected to the subscriberline 38, or the tenth line in the third group of ten lines, the linecircuit 28' operates to cause the finderconnector link previouslyassigned by the link distributor or allotter in the common equipment GMto the calling line, to be set into operation to seize the calling line.Assuming that the link 388 is assigned by the link distributor to set upthe connection, the finder switch 288 of the link operates to select thecalling line and to connect it through to the conductors of the linkline incoming to the connector switch 588 of the link. When the callingline 28 is seized and extended by way of the finder switch 288 to theassociated switch 588, it is marked as busy in all of the otherconnector switches of the links, and the control equipment of the seizedlink is automatically conditioned to respond to the impulses of thefirst digit transmitted from the impulsing device provided at thecalling telephone station IB. Since the subscriber lines are of themulti-party type, provisions are made for selectively signaling thedesired called telephone station on any selected subscriber line. Withthe arrangement to be described more in detail hereafter, coded ringingis paratus included in the link circuit functions to test this line forthe purpose of determining the busy or idle condition thereof. If thecalled line is busy, busy tone current is applied tothe link line andreturned over the loop to the calling telephone station to indicate tothe party at the calling telephone station that the desired connectioncannot immediately be completed.

On the other hand, if the called line is idle at the time it isselected, the code selecting or ringing digit which is dialed at thecalling telephone station, causes a selected coded ringing current to beapplied to the side of the line to which the ringer of the telephonestation ID is connected, the code of the selected ringing currentcorresponding to the called telephone station vID. While each of theringers of the telephone stations included in the group of telephonestations with the telephone station ID are operated, the character ofthe code ring indicates that the telephone station ID is the telephonestation being called. During the ringing operation, ringback tonecurrent is applied to the loop extending to the calling telephonestation to indicate to the party at this station that the desired calledtelephone station is being signaled.

Finally, a connection between the calling and called telephone stationsis completed when the I call is answered at the called telephone stationtioned to operate ID. As pointed out with particularity hereinafter, thearrangement of the link circuit apparatus is such that a link utilizedin setting up a desired connection is released only when the connectionis cleared out at the calling telephone station.

In extending a call initiated at one of the telephone stations to one ofthe telephone stations connected to a subscriber line included in thefirst, eighth, ninthor tenth group of ten lines, a predetermined prefixdigit, a corresponding tens digit, a corresponding units digit, and acorrespnding code ringing digit are dialed, in the order named, at thetelephone station initiating the 'call. For example, when a subscriberat the telephone station IB initiates a call, by lifting his receiverfrom its switch hook, which is to be extended to a telephone stationconnected to a particular subscriber line included in the first group often lines, the line circuit 20 operates and causes the finder-switch ofa previously assigned finder-connector link to be operated to seize thecalling line, as previously, explained. When the predetermined prefixdigit is dialed at the calling telephone station IB, the seized link iscondiits connector switch to select the first, eighth, ninth or tenthgroups of ten lines. Thereafter the connector switch responds -'group often lines,

dialing of the units digit, corresponding to the particular subscriberline to which the called telephone station is connected, to select thecalled subscriber line from the selected group of ten lines. Theoperation of the system to test the selected line for the purpose ofdetermining the busy or idle condition thereof and to apply busy tonecurrent to the link line in the event that the selectedline is busy isthe same as that previously described. Also, the system operates, asdescribed above, to cause a selected coded ringing current,corresponding to the called telephone station, to be applied to the sideof the line to which the ringer of the called telephone station isconnected upon dialing the code selecting digit at the calling telephonestation IB. A connection between the calling telephone station I B andthe called telephone station connected to. the particular line in thefirst group of ten lines is completed when the call is answered at thecalled telephone station.

The switching apparatus located in the exchange Ill may also be utilizedin setting up a connection between two telephone stations connected tothe same subscriber line, the sole function of the apparatus in thisregard being that of selecting and applying ringing current to thecalling line of the proper code to signal a party at the calledtelephone station. Carrying out .this function necessitates the seizureof the calling line by an idle link, in the manner described above.Thereafter, and following the dialing of the digits of the directorynumber of the called telephone station at the calling telephone station,the calling party replaces his receiver upon its switch hook. When thecalling party hangs up, the finder switch of the operated link isreleased and ringing current of the selected code corre telephonestation. Finally, the-line circuit of the line in use is released whenthe connection is cleared out at the calling and called telephonestations.

As heretofore pointed out, the inter-office trunk lines are arranged intwo groups. More specifically, the first group is included in the secondand the second group is included in the third. group of ten lines. Inthe operation of the link to select one of the first group ofinter-office trunk lines including the line 2| interconnecting theexchange 10 and the exchange y one predetermined digit -or comprising apredetermined number of impulses is dialed at the calling telephonestation. The connector switch of the seized link responds to theimpulses of this one digit to select a previously assigned'idleone ofthe first group of trunk lines, More specifically, these inter-ofiicetrunk lines have associated therewith apparatus for setting up idle onesof the lines for selection by the connector switches, which apparatusfunctionsto assign an idle line for use immediately ductors are providedin character and after a. previously assigned line is takenior use.Hence, at the conclusion of the predetermined trunk selecting digitdialed at a calling telephone station, the connector switch oi! theseized link immediately operates to select the previously assigned idletrunk line. When the trunk line is selected, the calling line isswitched through by way of the selected trunk line and its associatedrepeater circuit to the terminating apparatus located in the exchangeI85. In this connection, it is pointed out that two sets of link lineconthe link circuit of each link, one set of which is devoid of allvoice frequency coupling elements such, for example, as condensers orrepeating coils, and is utilized in extending a connection by way of oneor the trunk lines. Following the extension of the connection to thetrunk line terminating apparatus located in the exchange I85, theconnection may further be extended to a desired called telephone stationsuch, for example, as the telephone station A, by dialing the connectionis released following the establishment of a connection to the telephonestation A depends upon the nature of the repeater circuit associatedwith the trunk line which is used in setting up the connection.

Since the trunk lines interconnecting the exchanges I and I85 are ofthe'two-way type, it will be understood that any one of these lines ofthe switching apparatus included in the exchange I I! may be utilized inthe completion of calls originating or extended by way of the exchangeI85, and which are to be extended to one of the subscriber linesterminating at the exchange Ill. The mode of operation of the equipmentin the exchange I0 following the extension or a call thereto by way ofone of the lines in the first group of trunk lines is substantiallysimilar to that set forth with reference to the connection establishedbetween the telephone stations IB and ID.

In the operation of the link to select one of the second group ofinter-oflice trunk lines including the line 3i interconnecting theexchange I0 and the exchange I86, only one different predetermined digitX comprising a predetermined different number of impulses is dialed atthe calling telephone station, The operation and arrangement of thisapparatus for selecting an idle one of the trunk lines in the secondgroup of inter-ofiice trunk lines are otherwise the same as that of theapparatus for selecting an idle one of the trunk lines in the firstgroup of inter-oflice trunk lines, as described above.

As heretofore pointed out, the P. B. X-trunk lines are arranged in twogroups. The first group is included in the ninth group of ten lines, andthe second group is included in the tenth group of ten lines. To select.an idle one of the first group of P. B. X trunk lines, the number P, X,Y, R is dialed at the calling telephone station, the digits P, X and Ybeing different in the digit R being any desired ringing digit. Morespecifically, the number 8911 is dialed at the calling telephonestation. When the prefix digit 8 is dialed, the seized link isconditioned to operate its connector switch to select the first, eighth,ninth'or tenth group of ten lines. Thereafter the connector switchresponds to the tens digit 9 to select the ninth group of ten lines.Thereafter the connector switch responds to the units digit 1 to selecta previously regular directory number corresponding to the line to whichthe telephone station A is connected. The manner in which the assignedidle one of the first group of P. B. X trunk lines. More specifically,the first group of P. B. X trunk lines have associated therewithapparatus for setting up idle ones of the lines to be selected, whichfunctions to assign an idle trunk line for use immediately after apreviously assigned trunk line is taken for use. Dialing of the ringingdigit 1 causes coded ringing current corresponding to the code ringingdigit 1 to be applied to the selected P. B. X trunk line in order tosignal the operator at the private branch exchange connected thereto. Aconnection between the calling telephone station and the operator'sstation at the private branch exchange is completed when the call isanswered at the operators station.

As indicated above, only a portion of the lines of the ninth group areP. B. X trunk lines, the remaining lines of this group being subscriberlines. The connector switch arrangement is such that when the digits P,X, and X or Z are dialed into one of the connector switches one of thesubscriberfs lines of the ninth line group is selected. For example, ifthe number 899 or the number 896 is dialed at a calling telephonestation the connector switch of the assigned link responds by selectingthe particular subscriber line of the ninth line group corresponding tothe units digit 9 or 6.

In order to select an idle one of the second group of P. B. X trunklines the number 8011 is dialed at the calling telephone station. Theoperation and arrangement of this apparatus for selecting an idle one ofthe second group of P. B. X trunk lines are otherwise the same as thatof the apparatus for selecting an idle one of the first group of P. B. Xtrunk lines described above.

Considering now in greater detail the appara tus embodied in theexchange I II and involved in the above-described sequence ofoperations, and

referring to'Figs. 1 to 8, inclusive, 10 and 11 of the drawings, thereare illustrated the elements of the line circuits 2|, 3|, andterminating the lines 2|, 20, 3| and 30, respectively, the elements ofthe finder-connector link 300, and the elements of the distributor andcommon equipment 89L lustrated those portions of the ringing, tone andtiming apparatus understanding of the operation of the system. The linecircuits individually terminating the subscriber and trunk lines are ofmore or less conventional arrangement. the line circuit 20' terminatingthe subscriber line 20, comprises a line relay RI25, a cut-off relayRIM, and a line lock-out relay RI I5 connected and arranged to operatein the usual manner. The corresponding relays of the line circuit 30'terminating the subscriber line 30 are indicated at Rl55, RIM, and RI45,respectively.

The line circuits individually terminating the respective trunk linesare identical in character and circuit arrangement. More particularly,the line circuit 2| terminating the inter-oifice trunk line 2| comprisesa line relay RI III, a cut-oif relay Rl05, and a line l0ck-out relayRIM. The corresponding relays of the line circuit 3| terminating theinter-oflice trunk line 3| are indicated at RIM], Rl and RI30.

Each of the finder switches is of the fully directive all relay type,group and unit relays being provided for performing the line selectingfunctions. The lines terminating at each finder switch are arranged ingroups of ten lines and the lines of each group terminate at the contactMore particularly,-

There are also diagrammatically il- 890 which are essential to ansprings of one group R000 and one subgroup or gang relay. Morepartieularly, the finder switch 200 comprises ten group or gang relayscorresponding to and including the two relays R210 and R000 individuallyhaving contact springs for terminating the conductors of ten lines.While the group relays may he of any'desired commercial type having therequired number of contact springs, preferably these relays are of theimproved form disclosed and claimed in the copendlng application SerialNo. 109,813, Herbert F. Obergfell, filed November 9, 1936. The lines ofeach group are divided into two equal mibgroups respectively comprisingthe odd numbered lines and the even numbered lines, and, through theprovision of a subgroup relay in each finder switch, a group of fiveunit relays is sufilcient to permit the selection of any desired one ofa selected group of ten lines. Thus, the finder switch 200 comprises asubgroup relay R225, and five unit relays R200, R200, R2 I0, R2" andR220, each of which unit relays is operative to select either of twolines in a selected group of ten lines depending upon the operated ornoncperated condition of the subgroup relay R220. The finder switch 200also includes a pair of switching or control relays R200 and R200 whichare arranged to be controlled by way of the common equipment Iillustrated in Fig. 6, and are operative to initiate the operation ofthe finder switch to seize a calling line.

The common equipment "I shown in Fig. 6

includes a plurality of first auxiliary relays which are arranged to beenergized over start circuits controlled by the line circuitsassociatedwith the I respective lines terminating at the exchange l0.

These relays are selectively operative in response to the selectivecompletion of the start circuits and individually function to conditionfor operation a particular grouprelay embodied in the finder switch ofan assigned link. hlore particularly, ten first auxiliary relaysincluding the three relays R000, R0l0 and R020 are provided, whichindividually correspond to the gang relays embodied in the finder switchof each link. A group of five second auxiliary relays R000, R000, R000,

R000 are similarly provided which individually correspond to the unitrelays embodied in the finder switch of each um: and are operativetocondition the corresponding unit relays 'in the finder switch of an linkfor op-.

eration. 'Ilie energization of the subgroup relay in the finder switchof an-assigned link is dependent upon the operated or non-operatedcondition of a third ahxiliaryrelay R000 provided in the commonequipment, this latter relay also beingarranged to. be energi'ledoverthose of thestartcircults which are adapted to be coinpleted in the linecircuits terminating the lines included in predetermined ones of .theline subgroups. the arrangement or the appar'atus is such that when acalling condition is created on .one of the hues terminating at theexchange, start circuits are completed by the line relay associated withthe calling linefor causing the operation of the-one of the firstauxiliary relays R000, R0l0, etc., which corresponds to the group orlines including the calling line and for energizing the one of thesecondauxiliary e ays R000, R000, etc., which is operative to select theparticular calling line. If the calling line is in of its particulargroup the third 0118111017 completed start circuits, but if the callingline is in the other subgroup the third auxiliary relaymflisenergildmdoperlteltoouidiflonthc device operative in response relayR000 is not energized over the subgroup relay embodied in the finderswitch of the selected link for operation. In order to give the finderswitch of any assigned link ample time to seize the calling line towhich it is assigned and to connect the line through to the connectorswitch, of the link before the common equipment 09| is reconditioned torespond to another call, a relay R000 is provided, which relay isoperative immediately a link starts to seize a calling line andfunctions to open the operating circuits for all of the'auxillary relaysin the common equipment 001.

The link allotter or distributor 000 is illustrated in Figs. 2 and 6 ascomprising a group of ten allotter relays R200, R010, R000, etc., whichindividually correspond to the ten links corresponding to and includingthe link 000, two control relays R000 -and R010, a busy meter relay M000and an overflow meter relay M000. Each of the allottcr relayscorresponds to the allotter relay R200 and is operative to assign anidle one of the links to the use of the next calling line immediatelyafter a previously assigned link seizes a calling line and to preventthe assignment of the corresponding link to the use of a calling line.The allotter relays are operated successively to assign the links to theuse of calling lines; and after the tenth allotter relay of the groupoperates, the control relays R000 and- R010 are operated to recycle theallotter relays in order to provide for the reassignment of idle ones ofthe links and to operate the busy meter relay M000 if all of the linksare busy at this time. If all of the links are busy, 2. call initiatedat one of the telephone stations is not completed and the overfiowmeterrelay M000 is caused to operate.

Alarm apparatus 000 associated withv a pinrality of fault detectors.individual to the links is provided in the exchange for the purpose ofsignaling a supervisory operator in one of the distant exchanges any oneof the links. The alarm apparatus 000 comprises a start relay R000operative in response to an urgent fault in the link, a start relay R000operative in response to a non-urgent fault in the link, a local alarmor buzzer I, and a plurality of control relays R000, R000, R010 andR010. Each of the fault detectors comprises a device operative inresponse to the presence of a fault in the finder switch of the link, adevice operative in response to the failure of the ring pick-up relay tooperate in order to apply ringing current to a selected line, a deviceoperative in response to the presence of a hot coil in certain of therelays associated with the link, and a to an undercharged condition ofcertain of the batteries associated with the link. Thefirst aboveoperate to cause the operation of the start relay R000, while the lasttwo devices mentioned above operate to'cause the operation of the startrelay R000. The first-mentioned device includes a fuse link and isoperative to cause operation of the allotter relay corresponding to thefinder switch having a fault therein, thereby to prevent the allotter000 from assigning the finder switch to the use of calling lines, inaddition to causing in the event a fault appears in two devicesmentioned operation of the start relay R000. Each of the start relaysR000 and R000 is operative to initiate the operation ofthe alarmapparatus000 apply a characteristic tone current to the line I I for thepurpose of informing a supervisory operator as to the nature of thefault.

The link circuit proper is illustrated in Figs. 3, 4, 7 and 8 of thedrawings. The link line conductors CHM and Cl263 are arranged to beincluded in the operating circuit of the line relay R3l0. The line relayR3! 0 is of the usual impulse responsive type and in combination withthe two additional relays R305 and R3l5 forms an impulse correctingnetwork for repeating impulses transmitted thereto from a callingtelephone station over an impulsing circuit to the slow-toreleasecontrol relay R800 and the impulse counting relays illustrated in Figs.8 and .7, respectively. The link hold relay is indicated at R320. Therelay R350 is the usual switching through relay which is energized onlywhen the link is utilized in extending a connection by way of one of theinter-oflice trunk lines to one of the distant exchanges I or I86; Thecalled party answer relay is indicated at R365, this relay beingarranged to operate in the usual manner when a call is answered at acalled substation, and functions to control the operation of a slaverelay R330 which performs the battery reversing operation. For thepurpose of preventing the link from being permanently tied up throughseizure by a defective line or a line having a calling condition presentthereon for an unreasonable time interval, there is provided a linkrelease relay R300 and timing apparatus diagrammatically illustrated at310. This timing apparatus may be of any desired construction whichincludes means'for applying ground pulses to the conductor C|213 atspaced intervals, which normally retains ground on the conductor C1212,and which removes ground potential from the conductor Cl212 at intervalsspaced from the intervals during which ground potential is applied toC1213. If desired, this apparatus may comprise a commutator driven by asynchronous motor through a gear reduction box and including commutatorsegments suitably arranged to control the application of groundpotential to the two leads Cl!" and Cl213 in the manner described.

The counting relay network illustrated in Figs. 7 and 8 includes tenimpulse counting relays R to R180, inclusive, which relays. areseouentially operative in response to the impulses of each of aplurality of series of impulses transmitted to the connector switch 600and function to control the selection of a desired called line and tocontrol the selection of the code of the ringin current to be projectedover the called line. Each of the counting relays is arranged to belocked energized in series with a corresponding one of the three controlrelays R8l0, R820 and R830 and to be deenergized in response to theoperation of its succeeding counting relay in the manner described indetail hereinafter.

The ringing tone and timing equipment diagrammatically illustrated at800 comprises ringing apparatus 850 and a code interrupter I000. Thisapparatus is arranged in. a conventional manner, the ringing apparatus850 including a rin in generator from which ringing currentis derived,and the code interrupter apparatus 000 being connected alternately toimpress pulsating battery potential and ground potential on each of thefive interrupter leads Cl334 to Cl338, inclusive, for coded'intervalswhich are different .for each of the leads and comprise combinations ofshort and long pulsating battery impulses.

The switching relay R4|0 functions to connect the link line conductorsC|36l and Cl363, incoming to the link circuit, by way of voice frequencycoupling apparatus to the link line conductors C I28! and CI290,outgoing from the link circuit, to cause operation of a ring pick-uprelay R430 and to initiate the operation of the code interrupterapparatus I000. The switching relay R4l0 is controlled by the controlrelays R8l0, R820 and R830, which latter relays are controlled by thecounting relays R100, R1l0, etc., in their response to the impulses of acode selecting digit dialed at a calling telephone station. The countingrelays also select one of the interrupter leads to apply coded ringingcurrent to one side of the selected line, and control the operation of agenerator reversing relay R440 which functions to select the side of theselected line to which the coded ringing current is to be applied. Inorder to terminate the ringing operation when a call is answered at acalled telephone station there is provided a ring cut-off relay R450which is operative to terminate a ringing operation by causing thedeenergization,

of the ring pick-up relay R430.

The reverting call relay R400 cooperates 'with certain of the otherrelays to hold the connector switch 500 of the link 300 operated duringthe period when ringing current is being applied to a calling line on areverting call. Also, the reverting call relay R400 operates when apredetermined prefix digit is dialed at a calling telephone station tocontrol the operation of the prefix digid relay R340, which latter relaycontrols the prefix digit slave relay R460. These latter two relaysfunction to condition the connector switch 500 to select a line in thefirst, eighth, ninth or tenth groups of ten lines, as previouslyexplained. The busy relay R420 is provided for the purpose of causingbusy tone current derived from the busy and dial tone apparatus 040 tobe applied to a calling subscriber line when a selected called line isfound busy.

In order to rearrange the circuit connections so that the countingrelays are rendered effective to perform different duties during thesuccessive series of impulses transmitted thereto, two transfer relaysR410 and R480 are provided, in addition to the prefix digit relay R340and the prefix digit slave relay R460. More particularly, the relaysR340 and R460 are arranged to operate at the end of a first series ofimpulses corresponding to a predetermined prefix digit to connect thecounting relays so that predetermined ones of the group relays in theconnector switch of the link may be selected for energization; the relayR410 is arranged to operate at the end of the second series of impulsescorresponding to a tens digit to condition the counting relays to selectone of the unit relays in the connector switch of the,link forenergization and to condition the subgroup relay in the connector switchfor em ergization; and the relay R480 is operative at the end of thethird series of impulses corresponding to a units digit to condition thecounting relays to select the particular code of the ringing current tobe applied to the selected called subscriber line.

The connector'switch 500 of the link 300, including the apparatus forpreassigning idle ones of the interoflice and P. B. X trunk lines to beselected, is illustrated in Figs. 5 and 11. The connector switch per seis similar to the finder switch in that ten group or gang relays eachterminating the conductors of ten lines, five unit one of the linesreturns busy tone over relays, and a subgroup relay are provided forperforming the line selecting functions. Specifically, the connectorswitch illustrated comprises ten gang relays corresponding to andincluding the two relays R510 and.R580 illustrated, five unit relaysR520, R530, R540, R550 and R580, and a subgroup relay R500. Here again,the lines terminating at. the contact springs'oi each group relay aredivided into two subgroups and each unit relay is operative to selecteither of two lines, individually included indifferent subgroups,depending upon the operated or non operated condition of the subgrouprelay R500. Preferably, each of. the group relays R510, R580, etc., likeeach of the group relays of the finder switch 200, is of the formdisclosed and claimed in the copending application, Serial No. 109,813,Herbert F. Obergiell, filed November 9, 1936.

The apparatus for preassigning idle ones of the inter-oflice'trunk linesin the ten lines is common to all of the links and includes a group oftrunk select relays RI I 00\, RI I I0 and RI I20, which individuallycorrespond to the first, second and third inter oflice trunk linesterminating at the contact springs of .the second group relay R510, anda group of control relays RI I80, RI I82 and RI I84, which individuallycorrespond' to the inter-office trunks numbered from one to three in thesecond group of ten lines. As pointed out in greater detailhereinafter,'the two groups of relays cooperate in a manner such that anidle inter-ofllce trunk line in the second ten line group is preselectedand ready for the use of any one of the links so long as any of thetrunk lines in this group is idle, and when all of the trunk circuitapparatus of a link attempting to select the loop extending to thecalling subscriber.

The arrangement and operation of the apparatus for preassigning idleones of the interoflice trunk lines in the third group of ten lines aresubstantially the same as that of the apparatus for preassigning idleones of the interofiice trunk lines in the second group of ten lines, asdescribed above. This apparatus comprises a corresponding group of trunkselecting relays RII30 and RII40, and a corresponding group of controlrelays RI I88 and RI I88.

The arrangement and operation of-the apparatus for preassigning idleones of the P. B. X

trunk lines in the tenth group of ten lines are similar to that of theapparatus for preassigning idle inter-oillce trunk lines describedabove.

This apparatuscomprises a group of trunk selecting relays RII50, RI Iand RI I80 and a group of control relays RII80 and RII88 correspondingto the relays RI I50 and RI I 80. Also, apparatus (not shown)substantially the same as that described for preassigning idle ones ofthe P. .B. X trunk lines: in the tenth group of ten lines is providedfor preassigning idle ones of the P. B. x trunklines in'the ninth groupof ten lines.

Operation of the finder switch to extend a call initiated at. atelephone station connected to an odd-numbered line to an idle link Acall is initiated at a telephone station connected to an odd numberedline by removing the receiver of the telephone instrument from itsassociated switch hook, thereby completing a circuit between thetelephone station and the line relay individual to the odd numberedline. For example, a call initiated at the telephone A, the call isextended second group of lines become busy the link.

. cuit of the. assigned link 300.

2| is connected to the link 800, the line relay station A is-extended tothe finder switch, I82 in the automatic exchange I and from the latterto the selector switch I83 therein. Upon dialing the proper digit at thetelephone station from the selector switch I83 through the two-wayrepeater181 to the odd numbered inter-ofllce trunk line 2I, whereuponthe ,line relay RI I0 individual to the line 2| is operated. Theoperating circuit of the line relay RII'0 extends from ground at RIIO byway of the upper winding of RIIO, RAI08, the conductor CI200 of the line2I, the-repeater I81, the selector switch I83, the finder switch I82,the telephone instrument at the telephone station A, the finder switchI82, the selector switch I83, the repeater I81, the conductor CI20I ofthe line 2I,.RAI01 and the lower winding of 'RI I0 to battery. Assumingthat the link illustrated is the link assigned use of the calling line,the line relay RIIO, upon operating, completes at RAII2 an operatingcircuit for the auxiliary group relay R800, this circuit extending fromground at RAII2 by way of RAI02, CI2I2, the winding of R800, RA809,RA882, RA621, etc., RA8I1, RA801 and the resistor 883 to battery. Theline relay RI I0 also completes at RAII3 an operating circuit for theauxiliary unit relay R835, this circuit extending from ground at RA83Iby way of CI2I8, RAII3, RAI03, CI2I4, RA805, CI288, the windby theallotter to the ing of R835, RA539, RAGBI, RA658,RA853,RA848,

RA643, RA838 and the resistor 884 to battery.

Upon operating, the relay R800 completes at RA808 an obvious holdingcircuit for itself and prepares at RA808 gang relay R210 in RA242 theoperating circuit of the gang relay R210 and completes at RA248 theoperating circuit of the unit relay R200, the operating circuit of thegang relay R210 extending from ground at RA805 by way of CI235, RA242,CI22I and the winding of R210 to battery, and the operating circuit ofthe unit relay R200 extending from ground at RA838 by way of CI238,RA248, CI250 and the winding of R200 to battery. The relay R240 alsocompletes at RA25I a circuit for energizing the relay R880, this circuitextending from ground at R880 by way of the winding of R880, CI245,RA25I, CI258, the link conductorCl283 of the link 300, RA355, RA335 andthe upper winding of the line relay R3I0 to battery. Upon operating, therelay R880 interrupts at RA882 a point in the operating circuits of theauxiliary group relays R800, R8I0, etc., and interrupts at RA88I a pointin the operating circuits of the auxiliary unit relays R835, R840, etc.,thereby busying the allotter 800 so that it is non-responsive to othercalls.

The gang relay R210 operates to close its contact springs connected tothe lines numbered from 20 to 29 and the unit relay R200 operates toconnect the calling line 2-I to the link cir- When the line R3") isoperated, this circuit extending from ground at RAM 2 by way of the linkconductor CI282, RA352,'the link conductor CI26I, RA226, CI253, RA202,the contact springs of the gang relay R210, the conductor C|200 of theline 2|, the repeater I81, the selector switch I83, the finder switchI82, the telephone instrument at the telephone station A, the finderswitch I62, the selector switch I83, the repeater I81, the conductorC.|20| of the line 2|, the contact springs of the gang relay R210,RA203, CI255, RA221, the link conductor CI263, RA355, RA335 and theupper winding of R3I0 to battery.

Upon operating, the line relay R3I0 completes at RA3|| a circuit foroperating the link impulsing relay R305, this circuit extending fromground at RA323 by way of RA3II, and the winding of R305 to battery;interrupts at RA3I2 a point in the circuit extending from battery by wayof the upper winding of R3I0, RA335, the resistor 3|0' and RA3|2 to thelink control conductor C|264; and prepares at RA3I2 a point in thecircuit for applying ground to the control conductor C 264.

Upon operating, the link impulsing relay R305 completes at RA309 anobvious circuit for operating the hold relay R320, which is of the slow--to-release type, and an obvious circuit for applying ground to thecontrol conductor CI264, thereby to mark the link 300 as busy in theallotter. When the control conductor CI264 is grounded, the lock-outrelay RIM and the cut-off relay Rl05, individual to the line 2|, areoperated, the circuit for energizing these relays extending from thegrounded control conductor CI264 by way of RA228, CI251,'RA204, thecontact springs of the gang relay R210, the control conductor CI202 ofthe line 2 I, the winding of R|05 and the winding of RI to battery. Uponoperating, the cut-off relay RI interrupts at RAI06 and RA|01 theoperating circuit of the line relay RI I0. The line relay RI I0 thenrestores and interrupts at RAI I2 the holding circuit of the relay R600and interrupts at RAI I3 the holding circuit of the relay R635, and thelatter relays restore. The lockout relay R|00 operates and interrupts atRAI02 a further point in the holding circuit of the relay R600 andinterrupts at RAI03 a further point in the holding circuit of the relayR635. The presence of ground potential on the control conductor CI202 ofthe calling line serves to busy this line in the other automaticswitches having access thereto.

Upon operating, the hold relay R320 completes at RA322 a holding circuitfor itself, this circuit extending from ground at RA322 by way of RA3| 6and the winding of R320 to battery; applies at RA323 multiple ground tothe control conductor CI2-64 in order to retain the cut-off relay RI 05and the lock-out relay R|00 individual to theline 2| operated duringimpulsing periods; and completes at RA32| holding circuits for theoperated gang relay R210 and 'the operated finder unit relay R200. Theholding circuit of the operated gang relay R210 extends from ground atRA304 by way of 'RA32I, CI25I, the contact springs of R210 and thewinding of R210 to battery, while the holding circuit of the operatedunit relay R200 extends from ground at RA304 by way of RA32I, CIL5I,RA20I and the winding of R200 to battery.

The hold relay R320 also completes at RA325 a circuit for operating thestart relay of the dial ,and busy tone apparatus 840,- thls circuitextending from ground at RA325 by way of (H302,

RA4I9', the start lead C|3I4 and they winding of the start relay, notshown, in the dial and busy tone apparatus 840 to battery. The dial andbusy tone apparatus 840 then operates to apply dial tone to the link300, this circuit extending from pulsating battery in the dial and busytone apparatus 840 by way of the dial tone conductor CI346, RA414,RA462, RA424, RA4I4, the link conductor C|29|, the condenser C|29I andRA355 to the link conductor CI263, through the telephone instrument atthe telephone station A connected to the link conductors CI263 and C|26|by way of the finder switch 200, the line 2|, the repeater I81, theselector switch I83 and the finder switch I82, and from the linkconductor C|26I by way of RA352, the link conductor CI282 and RA4I2 toground. The party initiating the call at the telephone station A thenreceives dial tone indicating that a link has been seized and that hemay operate the dialing mechanism associated with the telephoneinstrument to extend the call from the link to the called line.

In a similar manner, when calls are initiated at telephone stationsconnected to the odd-numbered lines 23, 25, 21 and 29, respectively, therelay R600 and one of the relays R640, R645, R650 and R655,respectively, are operated in the auxiliary or common equipment. Therelay R600 operates the gang relay R210, and the relays R640, R645, R650and R655 operate the unit relays R205, R2I0, R2|5 and R220,respectively, in the finder switch 200 to connect the lines 23, 25, 21and 29, respectively, to the link 300.

Similarly, when calls are initiated at telephone stations connected tothe odd-numbered lines 3|, 33, 35, 31 and 39, respectively, the relayoperates the gang relay R260 and the relays R635,

R640, R645, R650 and R655 operate the unit -relays R200, R205,'R2|0,R2|5 and R220, re-

spectively, in the finder switch 200, to connect the lines 3|, 33, 35,31 and 39, respectively, to the link 300.

Operation of the finder switch to extend a call initiated at a telephonestation connected to an even-numbered line to an idle link A call isinitiated at a telephone station connected to an even-numbered line byremoving the receiver of the telephone instrument from its associatedswitch hook, thereby completing a circuit between the telephone stationand the line relay individual to the even-numbered line. For example,when a call is initiated at the telephone station IB connected to theline 20, the line relay RI25, individual to the line 20, is operated,the operating circuit of the line relay RI25 extending from ground atR|25 by way of the upper winding of RI 25, RA|2I, the conductor C|203 ofthe line 20, the telephone instrument at the telephone station IB, theconductor CI204 of the line 20, RA|22 and the lower winding of R|25 tobattery. Upon operating, the line relay RI 25 completes at RA|21 anoperating circuit for the relay R600 in the common equipment, thiscircuit extending from ground at RA|21 by way Upon operating, the relayR600 completes at RA606 an obvious holding circuit for itself, andcompletes at RA60I the series operating circuit of the relays R630 andR655, this circuit extending from ground at R630 by way of the upperwinding of R630, CI2I1, RAI28, RAII6, CI2I6, RA60I, C1265, the windingof R655, RA659', RA66I, RA656, RA653, RA646, RA643, RA638 and theresistor 664 to battery. Also, the relay R600 prepares at RA606 thecircuit for energizing the gang relay R210.

7 Although the relays R630 and R655 are energized in series, the relayR655 does not operate at this time due to the relatively high resistanceof the upper winding of the relay R630 connected in series therewith.However, the relay R630 operates and prepares at RA63Iv a circuit forenergizing the group unit.or subgroup relay R225 in the iinder switch200, and connects its relatively low resistance lower winding inparallel with its upper winding to cause the relay R655 to be operatedin series with the relay R630.

I Upon operating, the relay R655 completes at RA659 an obvious holdingcircuit for itself, completes at RA651 a circuit for energizing thecontrol-relays R230 and R240 in parallel and pre-' pares at RA656 acircuit for energizing the unit relay R220 in the finder switch 200. Theoperatrelays;

ing circuit of the relays R230 and R240 extends from ground at RA651 byway of CI241, RA262,

CI249' and the winding of R230 and R240 in parallel to battery.

Upon operating,the relay R240 completes at RA242 the operating at RA250the operating circuit of the group unit relay R225, and completes atRA249 the operating circuit of the unit relay R220; the operatingcircuit of the gang relay R210 extending from ground at RA606 by way ofCI235, RA242, CHM and the winding of R210 to battery; the operatingcircuit of the group unit relay R225 extending from ground at RA63I byway of CI244, RA'250,'CI255 and the winding of R225 to battery; and theoperating circuit 01' the unit relay R220 extending from ground at RA656by way 0! C I343, RA249, CI254 and the winding of R220to battery. Therelay R240 also completes at RA25I a circuit for energizing R560, thiscircuit extending from ground at R660, byway of the winding of R660,CI245, RA25I, CI256, the link conductor CI263 of .the link 300, RA355,

'RA335, and the upper winding of the line relay R3I0 to battery. Uponoperating, the relay R660 interrupts at RA662 a point in the operatingcircuits of R600, R6I0, etc., and interrupts at RA66I a point in theseries operating circuit of R630 and one of the relays R635, R640, etc.,thereby to busy the allotter 600 to other calls.

The gang relay R210 operates to close its contact springs to connectthe. lines between'20 and 29 through to the armature springs. of theunit the groupunit relay R225 operates to disconnect its armaturesRA226, RA221, RA226, RA229, from the conductor CI253, CI255, CI251, CI259, respectively, and to connect these armatures .to the conductorsCI254, C I256, CI256 and CI260, respectively; and the unit relay R220operates to connect the line 20 to the link circuit of the link 300.when the line 20' is connected through. to the link circuit, the linerelay' R3I0 is operated, this circuit extending from ground ,at RA4I2 byway of the link conductor CI202,

RA352, the link conductor CI26I, RA226, CI254, RA222', the contactsprings of the gang relay R210, the conductor CI203 of the line 20, the

telephone instrument at the telephone station IB, the conductor CI204 ofthe line 20, the concircuit of the gang relay 'The party initiating thecall tact springs of the gang relay R210, RA223', CI256, RA221, the linkconductor CI263, RA355, RA335 and the upper winding of R3I0 to battery.

Upon operating, the line relay R3I0 completes at RA3I I the above-tracedcircuit for operating the link impulsing relay R305, interrupts at RA3I2a point in the priming circuit for R3l0, and prepares at RA3I2 a pointin the path for applying ground to the control conductor CI264.

Upon operating, the link impulsing relay R305 completes at RA303 anobvious circuit for energizing the hold .relay R320 and for applyingground to the control conductor CI 264, thereby to mark the link 300 asbusy in the allotter and to mark the calling line as'busy. when thecontrol conductor CI264 is grounded, the lock-out relay RI I5 and thecut-oil. relay RI20, individual to the circuit of the relay R600 andinterrupts at RAI28' the series holding circuit of the relays R630 andR655, causing the latter relays to restore. The lock-out relay RII5operates and interrupts at RAI I1 a further point in the holding circuitof the relay R600 and interrupts at RAI I8 a further point inthe seriesholding circuit of the relays R630 and R655.

Upon operating, the hold relay R320 completes at RA322 a holding circuitfor itself, completes at RA323 a path for applying multiple ground tothe control conductor CI 264 in order to retain the cut-ofl relay RI20and the lock-out relay RI l5, individual to the line 20, operated duringimpulsing periods, and completes at RA32I holding circuits for theoperated gang relay R210, the operv ated group unit relay R225 and theoperated unit relay R220 in the finder switch 200. The holding circuitofthe operated gang relay R210 extends from ground at RA304 by way ofRA32I, C I25I, the contact springs of R210 and the winding of R210 tobattery. The holding circuit 'of the operated group unit relay R225extends from thegrounded conductor CI25I by way 'of RA229' and thewinding of R225 to battery, while the holding circuit of theoperatedunit relay R220 extends from the grounded conductor CI25I by wayof RA22I and thewinding of R220 to battery.

The hold relay R320 also completes at RA325 a circuit for energizing thestart relay, not shown, of the. dial and busy tone apparatus 040,thereby to initiate the operation of this apparatus to return dialtoneto the telephone instrument at the telephone station IB aspreviously explained. at the telephone station IB upon receiving dialtone is informed that a link has been seized andthat he may operate thedialing mechanism associated with the telephone instrument to extend thecall from the link to the called line.

In a similar manner, when calls are initiated at telephone stationsconnected to the even-numbered iries 22, 24, 26 and 26, respectively,relay R600, the relay R630 and one of the relays R635, R640, R645 andR650, respectively, are operated in the common equipment. The relayR600, causes the operation or the, gang relay R210; the relay R630'causes the operation of the

